1. Field of the Invention
The present invention relates to a process for producing an alkyl nitrite. More particularly, the present invention relates to a process for producing an alkyl nitrite by reaction of nitrogen oxide with an alkyl alcohol with high efficiency and high industrial stability, while effectively removing the resultant heat generated by the reaction.
The alkyl nitrite produced by the process of the present invention is useful for the production of a dialkyl oxalate by reaction of the alkyl nitrite with carbon monoxide or production of a dialkyl carbonate from the alkyl nitrite by a non-phosgene method.
2. Description of the Related Art
As methods for producing nitrite esters, Japanese Examined Patent Publication No. 61-6,057 and No. 61-26,977 disclose preparation of methyl nitrite by reacting an alcohol with nitrogen oxide in the gas phase in a production process of dimethyl oxalate, and Japanese Examined Patent Publication No. 62-47,867 and No. 63-35,617 and Japanese Unexamined Patent Publication No. 6-25,104 disclose preparation of nitrite esters by reaction of alcohols with nitrogen oxide in a gas phase.
In the reaction of a lower alkyl alcohol, for example, methyl alcohol, with a nitrogen oxide gas containing, as a principal component, nitrogen monoxide, however, a large amount of heat of reaction is generated in accordance with the following reaction: EQU NO+ROH+1/4.multidot.O.sub.2.fwdarw.RONO+1/2H.sub.2 O
Accordingly, to prepare the nitrite ester in a high yield at a high degree of safety, it is important that the reaction temperature be closely controlled within an appropriate temperature range, and a reckless run of the reaction due to the reaction heat be prevented. However, the above-mentioned prior publications are completely silent as to concrete means for removing the reaction heat and for appropriately controlling the reaction temperature, and therefore the industrial production of nitrite esters by the above-mentioned prior art was very difficult.
In Japanese Unexamined Patent Publication No. 6-298,706, it is described that the reaction heat can be removed and the reaction temperature can be controlled by injecting an alcohol liquid into a reaction region in which the nitrite ester is produced, to remove the reaction heat by a latent evaporation heat of the alcohol.
In the removal method of reaction heat in accordance with Japanese Unexamined Patent Publication No. 6-298,706, however, the reaction temperature may not always be controlled in the production of the nitrite ester, or the above-mentioned reaction may not be appropriately and fully maintained. Therefore, the production of the nitrite ester was very difficult to effect on an industrial scale and with a satisfactory reproducibility. Japanese Unexamined Patent Publication No. 1-121,251 discloses a process for producing an alkyl nitrite, and a reaction vessel for the process. In this process, a nitrite ester (an alkyl nitrite) is produced by reacting nitrogen oxide with a lower alcohol and oxygen in a reaction region including at least two sections, namely a reaction section in which a gas/liquid contact procedure and a cooling procedure are carried out, and a refining section in which a vapor-residing time long enough to enhance the conversion of oxygen be obtained and a refining capacity large enough to reduce the contents of water and nitric acid in the reaction gas.
Further, Japanese Unexamined Patent Publication No. 1-121,251 discloses concrete means for removing heat from the reaction vessel, namely, a means for withdrawing a liquid side flow from a lower packing section, a means for cooling the liquid side flow, and a means for returning the liquid side flow into the reaction vessel.
The process and apparatus of Japanese Unexamined Patent Publication No. 1-121,251 is disadvantageous in that even when the above-mentioned cooling means is used and the reaction of nitrogen oxide with an alcohol is carried out, although the removal of the reaction heat can be effected with a certain extent, the nitrite ester cannot be obtained in a high yield with a satisfactory degree of stability, and/or by-products, for example, nitric acid, are produced in a large amount, and thus the above-mentioned reaction cannot be stably carried out with a high efficiency.